Workers go through training at the Concord call center in Concord, Calif., on Thursday, Sept. 26, 2013. On Oct. 1, the Concord call center will start enrolling people into the Affordable Care Act. About 155 employees currently work at the North Concord site. (Susan Tripp Pollard/Bay Area News Group)

The Concord call center where agents offer advice on health coverage available under the Affordable Care Act is about as nice a facility as an office workplace can be.

Dozens of oversized cubicles, most equipped with two computer screens, are spread out across 37,000 carpeted square feet. A floor-to-ceiling glass wall running the length of the room lets the sunlight stream in as busy fingers clatter at keyboards. It's an energized environment that seems ready for any challenge.

Good thing.

Beginning Tuesday, according to officials at Covered California -- the state insurance exchange that oversees the operation -- the center can expect to field an average of 4,000 enrollment inquiries daily. Recently trained agents who've never done this before will explain a program that never existed before to a public that largely doesn't understand it.

"It's a big challenge," said spokeswoman Angie Blanchette. No kidding.

Up until now, the 135 agents -- culled from 7,000 job applicants -- have split their time between learning the details of what's offered and answering questions from curious callers. Now enrollment begins in earnest, and there's a lot to understand.

"There are 12 different insurance companies with different plan levels," said agent Christopher Kisak, who knows about the importance of health coverage. He was uninsured when he suffered a heart attack five years ago and ran up a $176,000 bill that hung over his head until he negotiated a settlement.

"We'll ask their income. We'll ask their family size. We input that into an online calculator and find out how much of a subsidy they are eligible for."

Reduced premiums are available to applicants earning between 138 and 400 percent of the federal poverty level -- only the federal government would round off anything to 138 -- and Medi-Cal coverage is available to applicants earning less than that.

Plans are available at four coverage levels -- Platinum (which covers 90 percent of expenses), Gold (80 percent), Silver (70) and Bronze (60) -- the costs of which are affected by where the insured lives and how many family members are covered. There's also a choice of HMO, PPO or EPO plans among a dizzying array of options.

Kisak said many of his early callers were confused, and few were even angry, including one man who "read me the riot act" when he learned he was ineligible for subsidies and would have to pay full fare. When he finished venting, Kisak asked him what kind of coverage he currently had.

"I offered him the same coverage at half the price," Kisak said. "He said he'd call back when enrollment began."

Agent Salvador Sanchez said the program's biggest hurdle is getting the word out. He and his colleagues have spent more than six weeks in training, learning how to navigate the complexities and benefits of the plan.

"A lot of people haven't opened the door to look inside," he said. "They need to do that by calling us (888-975-1142). This is all about helping more people afford care."

Judging by the preliminary calls -- estimated at 1,500 per day -- there will be some questions that not even trained agents can anticipate.

Kisak smiled as he recalled one: "A person called in and wanted to know if we insured pets."